A bicycle library is a place where you can borrow a bicycle, just like you borrow a book from a regular library. Imagine that you want to ride a bike but you don't own one, or you want to try out different kinds of bikes before deciding which one to buy. A bicycle library is a great option for you!
At a bicycle library, they have all kinds of bikes for all ages and sizes, and they take care of them so they are safe to ride. You can sign up for a membership, just like at a regular library, and then you can borrow a bike for a certain amount of time. You can ride it around as much as you want, and then you return it when your time is up.
The people who work at the bicycle library can also help you fix your own bike if it's not working properly, and sometimes they organize fun events and rides with other people who also use the library.
So, to summarize: a bicycle library is a place where you can borrow a bike like a book, use it for a while, and then return it. It's a great way to try out different bikes or get more exercise without having to own a bike yourself.